1) Field of the Invention
This invention relates to light projectors. More particularly it relates to light projectors having optical components, such as retarder foils, polarizers, beam splitters, and light valves.
2) Description of the Related Art
Optical projectors are common devices that are used to produce images on a screen. Such projectors are finding wide spread use as television displays, computer screen displays, and theatre displays. Optical projectors, particularly liquid crystal optical projectors, are beneficial because they produce large images using relatively small, inexpensive devices.
Typical liquid crystal optical projectors include a light source that illuminates an optical projection system. Such optical projection systems usually include an input optical subsystem having a first window, an input lens that collimates and focuses the illuminating light, and a polarizing prism. The polarizing prism selectively reflects the portion of the focused light that has the correct polarization direction experienced by off axis light rays, while the reflective liquid crystal light valve selectively changes the polarization of the light that is reflected back through the second window and into the prism. The prism then passes the portion of the light that has changed polarization through a third window onto the display screen.
While generally successful, typical optical projection systems have problems. First, the light from the light source passes through a large number of optical elements, each of which increases cost and each of which can produce undesirable birefringence. Furthermore, the various windows often require relatively expensive antireflective coatings on one or more optical surfaces. Also, the prism tends to be relatively expensive and tends to have imperfections that are detrimental to overall operation. Another problem relates to the alignment of the optical components. Thermal differences across the system can produce significant optical path length changes that can have detrimental effects on overall system performance.
Therefore, a new optical projection system would be beneficial. Even more beneficial would be a new optical projection system that reduces the number of optical components. Even more beneficial would be an optical projection system that reduces thermal differences, and that reduces the need for antireflective coatings.
The principles of the present invention enable optical projection systems having a reduced number of optical components. The principles of the present invention also enable optical projection systems having reduced thermal differences. The principles of the present invention further enable optical projection systems that do not require antireflective coatings.
An optical projection system in accord with the principles of the present invention includes a polarizer, a polarizing beam splitter, and a reflective light valve immersed in a liquid, such as water, contained in a housing. Beneficially, the housing also includes an input lens, such as a spherical lens, an exit window, and a light valve. Also beneficially, the light valve includes a retarder foil.